This invention relates to a tire testing device and a method for testing a tire.
From EP 1 043 578 A2 there is known a tire testing apparatus for the interferometric testing of a tire, comprising a vacuum chamber and one or more measuring heads. With this tire testing apparatus a testing method is carried out, in which the surface contour of the tire is compared with each other in two different states. The different states are generated by a change of the pressure or negative pressure in the vacuum chamber. The tire thereby experiences a load change, which at defective points effects a significant change of the surface contour, by which the defects in the tire can be determined.
To be able to perform this in a reliable and accurate manner, care must be taken that a change in contour which is not due to the change in load is avoided. This can be achieved by a construction of the tire testing apparatus as insensitive to vibrations as possible, which prevents disturbances and changes in position of the measuring head and/or the tire. Tensions and creep movements of the tire are attenuated as far as possible by the stable support thereof. Too strong own movements of the tire can lead to disturbances in the result images up to an exceedance of the narrow measurement range of the interferometric measurement.
In the interferometric testing apparatus known from EP 1 043 578 A2, the tire therefore is tested lying on its side wall, in order to ensure a rather full-surface support of the tire and in this way minimize vibrations and own movements. After positioning the tire, a waiting time may be required, which is dependent on the weight, size and inner structure of the tire as well as the introduced forces required for positioning the tire. Only after expiration of this waiting time testing can be started, in that the one or more measuring heads test the tire section by section. Usually, the tread is tested from inside in individual sectors, and the bead and the side wall are tested from outside in individual sectors. The measuring head typically is moved relative to the tire along the circumference of the tire, so that the entire tread and a side wall can be tested one after the other.
Thereafter, the tire must be lifted and turned over, in order to be able to also test the second side wall. This involves a considerable effort in large and heavy tires, which can have a weight of up to several tons. While being turned over, the tire experiences forces which can lead to renewed, slowly decreasing changes in contour. This may require a renewed waiting time before testing the second side wall.
To avoid this disadvantage, EP 1 355 142 A2 proposes to test the tire in a vertical, i.e. upright position. In this position, both side walls can be tested without turning over the tire. For testing the tire, one portion each is tested and subsequently the tire is turned on. In this way, the entire tire can be tested. For rotating the tire rollers are provided, on which the tire rests with its rim hole or with its tread.
In the process, however, the tire experiences non-uniform forces which can lead to pressure marks and whole-body deformations. Before interferometric testing, a waiting time also must be observed here, until these disturbances have decreased. After each rotation of the tire for testing the next section, new force relations exist, which necessitate further waiting times in part lasting several minutes.
From DE 203 14 939 U1 a tire testing apparatus is known, in which the tire is tested in vertical position, wherein the measuring heads can be moved along the side walls, in order to inspect various points of the tire. In the process, the tire is suspended on rollers on which it rests with its bead. This arrangement on the one hand involves the disadvantage of an ongoing deformation of the tire. On the other hand, the bearings inside the bead impede the optical and mechanical accessibility of the tire interior. The measuring head for observing the inside of the tire at the upper position cannot be brought into the ideal measurement position without obstacles. The upper inside of the tire is hidden by the bearings for a considerable part and therefore cannot be detected completely.